The output voltage of a voltage source type power conversion system is with few harmonic components and high output capacity, so the voltage source type power conversion system is suitable for applications involving medium or high voltage, and has been widely applied in modern industry. In the same input voltage and output voltage, compared with a general cascaded high voltage conversion system, a voltage source type power conversion system has a higher voltage jump, thus a common-mode voltage of the source type power conversion system is more serious. The common-mode voltage of the voltage source type power conversion system generates current to ground or motor bearing current through the coupling capacitance between the stator and the rotor of a motor, while a large bearing current will probably affect the service life of the motor, as well as leading to grid-to-ground voltage being increased, thereby affecting the operation of other equipments. In view of the hazard of common-mode voltage, how to reduce the common-mode voltage of a power conversion system has become a focus of industrial circles and universities. Conventionally, to eliminate the common-mode voltage of a voltage source type power conversion system, the voltage endurance capability of an isolation transformer is enhanced to bear the common-mode voltage, which makes the volume of the isolation transformer larger, the costs higher and results in that the voltage source type power conversion system has a less efficiency, a reduced power density and reduced reliability, etc.
In modern industrial applications, in order to weaken the serious hazard to a voltage source type power conversion system by the common-mode voltage, passive common-mode voltage filters applied to voltage source type power conversion systems and methods for suppressing common-mode voltage have being studied to suppress the effects that common-mode voltage imposes on voltage source type power conversion systems.